A wide variety of diagnostic and other biochemical tests employ a reagent which undergoes a detectable colour change in the presence of the analyte. The reagent is often conveniently carried on a test strip. Optics may be provided to assist the comparison of the observed colour change with a standard colour chart. Alternatively, optical absorption may be measured at one or more selected wavelengths.
For example, in the particular field of immunoassays, internal reflection spectroscopy is used. According to this technique, a thin layer of sample material is established on a surface of a transparent optical element and measurements are made of internal reflection of light at the interface with the sample.
A drawback of many known analysis techniques is that they rely upon optical detection of emitted, reflected or transmitted light or fluorescence with subsequent signal processing providing the required measure of absorption. This is believed to have hindered the development of an analysis apparatus which is sensitive, compact and rugged. Under certain circumstances, where for example the analyte is potentially toxic or poses a microbiological contamination or health risk, it is also desirable to have analytical apparatus of a form which is disposable after each analysis.
U.S. Pat. No. 5,622,868 discloses a biochemical analysis device comprising a pyroelectric transducer in a strip form. The transducer is provided with thin film electrodes and one or more reagents are deposited on the transducer surface. The reagent undergoes a colorimetric change when it comes into contact with the analyte being detected. The analysis device is then typically inserted into a testing apparatus and the reagent is illuminated by a light emitting diode providing light of a predetermined wavelength. Absorption of the light by the reagent is detected as microscopic heating at the surface of the transducer and the electrical signal output from the transducer is processed to derive the concentration of the analyte being detected. Piezoelectric transducers may also be employed by the analysis device.
WO 2004/090512 A1 discloses a similar analysis device in which the migration of a coloured species towards the transducer surface can be detected by analysing the time delay between the pulsed irradiation of a sample with electromagnetic radiation and the subsequent microscopic heating of the transducer caused by absorption of the radiation by the coloured species.
The biochemical analysis devices of U.S. Pat. No. 5,622,868 and WO 2004/090512 A1 avoid the need for complicated optical detection systems and signal processing electronics and can therefore be manufactured in a single use, disposable form. However, a significant problem associated with biochemical analysis devices which comprise pyroelectric and piezoelectric transducers is that the transducers are very sensitive to mechanical movement and vibration, which environmental effects tend to lead to a high level of noise in the electrical output signal.
There is therefore a need for an analysis device comprising a pyroelectric or piezoelectric transducer for which noise caused by environmental effects is reduced.